PROJECT SUMMARY: Toxoplasma gondii is an intracellular parasite that has a particular tropism for the central nervous system (CNS) where it establishes a latent, encysted infection. This parasite can cause severe neurologic consequences and death in congenital infections or when reactivated in immunocompromised patients. Although the CNS has long been known to be the primary organ that harbors the encysted form of Toxoplasma, the CNS- parasite interaction is poorly understood. I have developed a proposal that will help me gain the scientific tools I need to become an independent, academic neurologist who studies the molecular mechanisms underlying this CNS infection. The goal of the research plan is to use the mouse model of toxoplasmosis in combination with site- specific recombination to understand how the cells of the CNS and different strains of Toxoplasma have specifically co-evolved to produce a variable immune response that results in a chronic CNS infection with or without concomintant encephalitis. Preliminary work I have done shows that by equipping Toxoplasma with a secretable Cre recombinase fusion protein, site-specific recombination will occur only in infected host cells. Specific aim 1 is to transfer this technology into more biologically relevant, cyst-forming Toxoplasma strains. The goal of specific aim 2 is to verify the intracellular nature of the latent cyst in the CNS and establish the lineage of the cyst- containing host cells. I will accomplish this goal by using immunohistochemistry and fluorescent confocal microscopy to evaluate brain sections of Cre-reporter mice chronically infected with Toxoplasma-Cre strains. Specific aim 3 then employs laser- capture microdissection to isolate the infected host cells determined in aim 2 in order to genetically profile these host cells on mouse genome expression arrays and ultimately determine how host cell modifications impact disease outcome. Understanding the molecular mechanisms that culminate in a chronic infection of the CNS will guide the development of drugs needed to actually cure toxoplasmosis, as well as identify novel gene targets for modulating the immune response in autoimmune diseases of the CNS.